1. Field of the Invention
The present invention relates to a small watercraft such as a personal watercraft (PWC) which ejects water rearward and hydroplanes as the resulting reaction. More particularly, the present invention relates to a cooling system of an engine or the like of the small watercraft.
2. Description of the Related Art
In recent years, so-called water-jet propulsion personal watercraft, which are one type of small watercraft, have been widely used in leisure, sport, rescue activities, and the like. The water-jet propulsion personal watercraft is configured to have a water jet pump that pressurizes and accelerates water sucked from a water intake generally provided on a bottom surface of a hull and ejects it rearward from an outlet port. Thereby, the personal watercraft is propelled.
In the water-jet propulsion personal watercraft, a steering nozzle provided behind the outlet port of the water jet pump is swung either to the right or to the left by operating a bar-type steering handle to the right or to the left, to change the ejection direction of the water to the right or to the left, thereby turning the watercraft to the right or to the left.
In a propulsion engine of the small watercraft including the water-jet propulsion personal watercraft, a temperature and a temperature distribution of the engine vary between the time when the engine is starting and when the watercraft is continuously driving with the engine throttle in a fully open or almost fully open position. This causes slight deformation of the engine. In particular, in the case of an engine designed to minimize a clearance between a piston and a cylinder bore for the purpose of reducing lubricating oil consumption or a piston lap noise, slight deformation of the cylinder bore would lead to a noise or the like.